Fabrication of zinc objects by dual phase casting

Details Fabrication of zinc objects by dual phase casting Fabrication of zinc objects by dual phase casting

1998-12-01

2001-11-27

Dunn, Tom (Department: 1725)

Metal founding

Process

Shaping liquid metal against a forming surface

C164S900000

Reexamination Certificate

active

06321824

ABSTRACT:

BACKGROUND OF THE INVENTION
There are numerous household objects, such as components in plumbing products, which have intricate shapes requiring costly manufacturing processes to create the component. Examples may include spouts for faucets made using low pressure permanent mold casting technology with brass. These components require extensive finishing operations to create a component with a smooth surface suitable for plating. An alternative for making this type of component more economically is zinc die casting. Unfortunately, there are inherent weaknesses in die casting zinc. Porosity, cold shot and an inability to deal with thick sections are known weaknesses of zinc die casting. Furthermore, the waterway of a plumbing fixture can not be zinc due to the corrosion problems associated with zinc.
A different type of casting process would theoretically address many of these weaknesses. This process is a variant of plastic injection molding. It will be referred to herein as dual phase casting because the injected material is in a two-phase mixture, i.e., part solid and part liquid. Casting machines and services for this process are available from Thixomat, Inc. of Ann Arbor, Mich., under their registered trademark Thixomolding®. This technique has been applied to magnesium as taught in U.S. Pat. Nos. 3,902,544, 4,694,881 and 5,040,589, the disclosures of which are incorporated herein by reference. However, this technology has not been developed for zinc as a starting material.
SUMMARY OF THE INVENTION
The present invention is directed to a zinc dual phase casting process which overcomes the problems of zinc die casting and produces a part that can be plated using conventional plating techniques. The process also allows utilization of all plastic injection molding techniques such as insert molding.
The specific alloy to be used is ZA-8, a commercially available zinc-aluminum alloy typically used as a die cast material. ZA-8 ingots are shredded into chip form for use as a feedstock. A coarse granular shape prepared at a feed rate of 0.65 inches per minute has been shown to be effective. The temperature profile of the barrel of an injection molding machine is maintained such that the primary solids content in the casting is approximately 8-10% by volume. Alternatively, as more fully described below, certain shapes may be more advantageously formed by ZA-12 alloy.


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